The operation of an internal combustion engine, such as, for example, a diesel, gasoline, or gaseous fuel drive engine such as a natural gas engine, may cause the generation of undesirable emissions. These emissions, which may include particulates and nitrous oxide (NOx), are generated when fuel is combusted in a combustion chamber of the engine. An exhaust stroke of an engine piston forces exhaust gas, which may include these emissions, from the engine. If no emission reduction measures are in place, these undesirable emissions will eventually be exhausted to the environment.
Research is currently being directed towards decreasing the amount of undesirable emissions that are exhausted to the environment during the operation of an engine and on improving engine efficiency. One such approach involves adjusting the actuation timing of the engine valves. For example, the actuation timing of the intake and exhaust valves may be modified to implement a variation on the typical diesel or Otto cycle known as the Miller cycle. In a “late intake” type Miller cycle, the intake valves of the engine are held open during a portion of the compression stroke of the piston. By holding the intake valves open during a portion of the compression stroke of the piston, the compression ratio of the engine is reduced while maintaining a high expansion ratio, which results in a temperature reduction of the fuel/air mixture within the combustion chamber. This improved thermal efficiency reduces the emission of NOx.
One system utilized to vary intake valve timing is described in U.S. Pat. No. 6,237,551 (the '551 patent) issued to Macor et al. on May 29, 2001. The '551 patent describes a diesel engine having an intake valve actuated by a cam of a cam shaft. A chamber of fluid under pressure is associated with each intake valve, located between the intake valve and the cam, and connected through a solenoid valve to an outlet channel. An electronic control means varies the opening time of the intake valve by opening the solenoid valve.
Although the valve actuation system of the '551 patent may provide some flexibility in the opening timing of the intake valve, it may be problematic. For example, hydraulic variable timing solutions may experience some inconsistencies at cold temperatures, for example, during cold engine start and during cold operating conditions. Since fluid such as, for example, lubricating oil, is may be more viscous when cold, the more viscous fluid may have more difficulty flowing through smaller conduits that may be used to operate a variable valve system, possibly resulting in unpredictable operation.
Further reduction in the amount of pollutants emitted to the atmosphere and improvement in engine efficiency can be realized by combining a charged air induction system with variable valve timing. One such system is described in U.S. Pat. No. 6,273,076 (the '076 patent) issued to Beck et al. on Aug. 14, 2001. The '076 patent describes an engine having camless electro-hydraulically controlled intake valves capable of modulating a supply of air to a combustion chamber. The engine of the '076 patent also describes a combined supercharger/turbocharger assembly for directing charged air to the combustion chamber.
Although the engine of the '076 patent may reduce the amount of pollutants emitted from an engine by combining a charged induction system with variable valve timing, the engine of the '076 patent may also be problematic. In addition to the difficulties that may be associated with hydraulically controlled valve actuation, the engine of the '076 patent may also have low efficiency because the air induction system includes a supercharger. Specifically, the supercharger does not utilize the energy available in the exhaust flow from the engine of the '076 patent and requires additional driving energy from the engine to turn the compressor.
The disclosed air and fuel supply system is directed to overcoming one or more of the problems set forth above.